The current generation two-dimensional laminate porous oxide ceramic matrix composites (CMC) have relatively low interlaminar strength properties. Three-dimensional CMC materials have higher interlaminar strength; however 3D materials are more expensive and have not yet been fully developed for commercial applications, such as for use in the hot gas path of a gas turbine engine. It is known to improve the interlaminar strength of 2D CMC materials by further densifying the porous matrix in a conventional manner with additional sinterable phase matrix material. Unfortunately, as porosity is decreased in such materials, there is a corresponding reduction in in-plane strength (reduced by more than half in some embodiments) and the material becomes brittle as the interconnection between the matrix and the fibers becomes stronger.
It is known in both oxide and non-oxide CMC materials to apply an interface coating material to the fiber prior to matrix formation in order to decrease the fiber-matrix interconnection. The interface material functions to deflect cracks forming in the matrix material away from the fibers, thereby preserving the fiber network strength and the resulting in-plane mechanical properties. Unfortunately, fiber tows that are coated with interface coating materials are more difficult and expensive to weave and the coatings tend to spall off of the fibers during weaving. Furthermore, no viable process has yet been demonstrated for solution coating of filaments in fiber form, since close-packed fibers in cross-over points are difficult to coat.